i'm having a trouble bridging my object
In Blender 2.8 the W key to open the Context menu has been replaced by the Right Mouse Button. As it is a Context menu you have to be in Edge select mode to have the Bridge Edge Loops option available. 


Edge select mode.
Select the two edges.
RMB to open the Context menu.
Choose the Bridge Edge Loop.


Another way which works in both vertex or edge select mode is to open the Edge menu and select the Bridge Edge Loop option from there.